|Lactobacillus bulgaricus, morphologically identical to Lactobacillus paracasei|
|Subspecies:||Lactobacillus paracasei ssp. paracasei
Lactobacillus paracasei ssp. tolerans
Collins, Phillips & Zanoni, 1989
Lactobacillus paracasei (commonly abbreviated as L. paracasei) is a gram-positive, facultatively heterofermentative species of lactic acid bacteria that are commonly used in dairy product fermentation and probiotics. L. paracasei is a bacterium that operates by commensalism. It is commonly found in many human habitats such as our intestinal tracts and mouths as well as sewages, silages, and previously mentioned dairy products. The name includes morphology, a rod-shaped (bacillus shape) bacterium with a width of 2.0 to 4.0μm and length of 0.8 to 1.0μm.
So far, thirty four different strains of L. paracasei have been isolated from a variety of environments. Sixteen of those strains have been isolated from dairy, ten from plants, and eight from human and animal gastrointestinal tracts. L. paracasei is genotypically and phenotypically indistinguishable from other members of its genus such as Lactobacillus casei and Lactobacillus rhamnosus. However, they are easily differentiated from each other by their fermentation profiles. Its fermentative properties allows it to be used as biological food processors and supplements for diets and medical disorders, especially in the gastrointestinal tract.
Although probiotics are considered safe, may cause bacteria-host interactions and adverse health consequences. In certain cases there is a risk of bacteremia when probiotics are used. Currently, the probiotic strain, frequency, dose and duration of the probiotic therapies are not established.
Lactobacillus paracasei is a gram-positive, facultatively heterofermentative, non-spore forming microorganism. The cells of L. paracasei are typically rod shaped, with a size range of 2.0μm to 4.0μm in width, and 0.8 to 1.0μm in length. The organism is nonmotile. L. Paracasei cells often have square ends, and may exist either in single form or in chains.
L. paracasei grows optimally in a temperature range between 10 and 37 °C. No growth takes place above 40 °C. The organism is able to survive for approximately 40 seconds in a maximum temperature of 72 °C. As L. Paracasei is facultatively heterofermentative: lactic acid is produced from most strains.
L. paracasei exist as a common inhabitant of the human gastrointestinal tract as part of the normal flora. Naturally fermented vegetables, milk, and meat may also contain strains of L. paracasei.
Lactobacillus paracasei belongs to kingdom Bacteria. L. paracasei is part of the division Firmicutes, and also belongs to the class Bacilli. The order and family are Lactobacillales and Lactobacillaceae respectively. The argument on the nomenclature of L. paracasei versus L. casei has been one of intense debate. Most of the species profiled as L. casei or L. paracasei have been found to be part of the same species. In 1989, it was proposed that L. paracasei be designated a subspecies (paracasei) to account for the species that it shares DNA homology with. It has been shown their names have been used interchangeably in scientific literature. 16S RNA sequence homology has confirmed the relatedness between these species.
Historically, the difference between Lactobacillus paracasei and other lactobacilli has been based on biochemical characteristics. There is an approximately 90% sequence identity between casei, paracasei, and rhamnosus. However, there are some differential criteria that are commonly used to differentiate between them. These differential criteria include nutritional requirements and growth environment. L. Paracasei has been found to show specific differences with other Lactobacillus spp. in that it is somewhat heat resistant, grows well in ripening cheese, and it has high proteolytic activity.
L. paracasei has been found to have 34 strains. These strains have been isolated from various countries around the world. Although there is a small correlation between phylogenetic relatedness and origin of isolation, currently there is not enough evidence to support direct proof of the relationship.
L. paracasei's genome contains circular DNA and varies slightly among the different strains isolated. On average, the genomes are 2.9 to 3.0 millions of base pairs (commonly abbreviated Mb). It has a GC-content between 46.2 and 46.6% and is predicted to encode about 2800 to 3100 proteins. The difference in the genomes of these strains lies in variant cell envelopes, secretory proteins, and polysaccharides. Many of the commonly coded proteins are cell-surface associated cell-wall hydrolases that protect the cell against apoptosis. These enzymes have been shown to provide cellular protection to human epithelial cells.
Genetic diversity for the different L. paracasei genomes was assessed using multilocus sequence typing (MLST) and amplified fragment length polymorphism (AFLP). MLST is a technique used for classifying microbes by the use of DNA fragments from essential genes of the organism. AFLP is a Polymerase Chain Reaction (PCR) tool used in DNA profiling to amplify a desired DNA fragment with the use of restriction enzymes and ligands.
Clinical and research applications
Lactobacillus paracasei has been identified as a bacterium that has probiotic properties. L. paracasei is a part of the normal human gut microbiota. L. paracasei IMPC2.1 may be a chemoprophylactic in gastrointestinal cells. Gastrointestinal cells are susceptible to apoptosis and cell growth from both heat-killed and viable IMPC2.1 strains. L. paracasei 8700:2 has been isolated from healthy human gastrointestinal mucosa and human feces. Strain 8700:2 was also found to inhibit Salmonella enterica and Heliobacter pylori, two pathogens commonly found in the gastrointestinal tract. Strain 8700:2 breaks down oligofructose and inulin, while also growing rapidly on both and producing lactic acid as the end product.
L. paracasei is a constituent in the therapeutic, nutritional treatment VSL#3. This proprietary, standardized, formulation of live bacteria may be used in combination with conventional therapies to treat ulcerative colitis.
The manipulation of the gut microbiota is complex and may cause bacteria-host interactions. Although probiotics are considered safe, when they are used by oral administration there is a risk of passage of viable bacteria from the gastrointestinal tract to the internal organs (bacterial translocation) and subsequent bacteremia, which can cause adverse health consequences. Some people, such as those with immune compromise, short bowel syndrome, central venous catheters, cardiac valve disease and premature infants, may be at higher risk for adverse events.
Currently, the probiotic strain, frequency, dose and duration of the probiotic therapy are not established. Live bacteria might not be essential because of beneficial effects of probiotics seems to be mediated by their DNA and by secreted soluble factors, and their therapeutic effects may be obtained by systemic administration rather than oral administration.
LAB (Lactic Acid Bacteria) were classified and grouped in the early 1900s after gaining scientists' attention after observing the bacteria's interactions in different foods, especially dairy products. In 1991, Martinus Beijerinck, a Dutch microbiologist, separated Lactobacillus as gram positive bacteria from the previously known LAB group. L. paracasei has been recently classified as a part of the Lactobacillus casei group of probiotics. However, it has no clear taxonomic position. The name L. paracasei was proposed for rejection in 1996 by Dicks, Duplessis, Dellaglio, and Lauer.
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